The present invention relates to an electron beam lithography apparatus and more particularly to a lithography control apparatus with improved reliability.
An electron beam lithography apparatus alternately assumes a beam blanking state and a beam unblanking state in order to draw or write a pattern on an object such as a semiconductor wafer with an electron beam. More specifically, first, the electron beam is placed in its blanking state by applying a voltage to an electrostatic electrode provided in an electron beam path in synchronism with disappearance of a pattern signal in order to deviate the electron beam away from a stop electrode aperture provided in the electron beam path. Next, the voltage applied to the electrostatic electrode is removed in synchronism with appearance of the pattern signal so that the object is irradiated with the electron beam passing through the stop electrode aperture for a predetermined time to thereby draw a pattern on the object. Thereafter, the beam blanking is performed again in synchronism with disappearance of the pattern signal, and so on.
As described above, the electron beam lithography apparatus draws a pattern with alternately repeated blanking and unblanking (exposure) states. Therefore, in order to satisfactorily draw a pattern, it is necessary to detect and control the number of times of irradiating the object with the electron beam (hereinafter referred to as the number of shots).
Conventionally, this shot number was detected by counting the number of times of turn-on and turn-off of the voltage applied to the electrostatic electrode. Therefore, the counted number of shots coincides with the number of shots instructed by a controller, but does not necessarily represent the result of pattern drawing actually effected. JP-A- No. 57-112026 (laid-open on July 12, 1982) shows a lithography apparatus in which the number of times of object irradiation is determined on the basis of a blanking signal.